The invention relates to a method of providing grooves in a substrate of a soft-magnetic, iron-containing material selected from the group consisting of ferrites, Ni-Fe alloys and Al-Fe-Si alloys.
In manufacturing magnetic transducer heads having cores consisting of a soft-magnetic, iron-containing material such as a ferrite, the ferrite for the core of the head should sometimes be provided with grooves. One of the known methods consists in grinding grooves in a set of ferrite blocks which are then bonded together. However, such a mechanical operation does not provide sufficient dimensional accuracy. This is the case in particular when manufacturing a video head which requires a high degree of accuracy. It is hence difficult to manufacture magnetic heads economically with the same characteristics. Moreover, mechanical operations cause defects and the magnetic properties of the ferrite deteriorate as a result of the stresses introduced. In this connection, it is to be noted that even the working of a magnetic ferrite by means of a laser introduces undesired stresses.
Methods which do not introduce stresses are wet chemical (and electrolytic) etching. In these methods, a concentrated acid, for example, concentrated phosphoric acid, is used.
A masking layer is provided on the (ferrite) article. The layer is then provided photographically with a desired pattern; selected portions being subsequently removed by the developing. In electrolytic etching, this is succeeded by dipping in an electrolytic cell in which the (ferrite) article and an electrode are dipped in an etching electrolyte bath opposite to each other and at a distance from each other and the (ferrite) article serves as a cathode, and in which etching takes place in the exposed zones. Of the ferrites, Mn-Zn ferrite can be etched in this manner but Ni-Zn ferrite, which has a lower conductivity, cannot be etched in this manner. (An extra problem of Ni-Zn ferrite is that it etches inhomogeneously in a wet chemical etching process). A disadvantage of electrolytic etching is that the electrolyte can creep below the masking layer beyond the boundaries of the pattern lines as a result of which a certain amount of undercutting or lateral etching may occur. Moreover, electrolytic etching is not suitable for etching relatively deep grooves because it is a so-called diffusion-restricted process.